How to remove illegal apt sources

My system is Ubuntu 16.04.3 on an arm64 machine. I share this system with my colleagues.

Now someone must do some change because when I execute sudo apt update, I always get the error as below:

E: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/xenial-security/main/binary-i386/Packages 404 Not Found
E: Failed to fetch http://us.ports.ubuntu.com/ubuntu-ports/dists/xenial/main/binary-i386/Packages 404 Not Found
E: Failed to fetch http://us.ports.ubuntu.com/ubuntu-ports/dists/xenial-updates/main/binary-i386/Packages 404 Not Found
E: Failed to fetch http://us.ports.ubuntu.com/ubuntu-ports/dists/xenial-proposed/main/binary-i386/Packages 404 Not Found
E: Failed to fetch http://us.ports.ubuntu.com/ubuntu-ports/dists/xenial-backports/main/binary-i386/Packages 404 Not Found

I've remove and recreate a new /etc/apt/sources.list with the us arm64 sources and sudo rm /etc/apt/sources.list.d/* but sudo apt update gave me the same error. Also I sudo rm -rf /var/lib/apt/lists/* but nothing changed.